Persistent airway infections are a major clinical problem for patients with cystic fibrosis (CF). These infections are particularly difficult to treat because conventional antibiotics often do not achieve adequate delivery to the site of infection and because the risk of inducing bacterial resistance often limits long-term therapies. IB-367 represents a new class of medications to treat respiratory infections. It is made from naturally occurring proteins and will be administered as a liquid for inhalation using a nebulizer. Recent research suggests that there is a high salt concentration in the airways of people with CF. The high salt concentration may block natural substances that help to protect the lungs, which may be a contributing factor in the development of chronic lung infections in patients with CF. IB-367 is a substance (a protein analog) that may help to protect the lungs from infections and works in spite of high salt concentrations. This is a phase 1, randomized, placebo-controlled, double-blind, multicenter study. The primary objective is to determine the safety and tolerability of ascending multiple doses of inhaled IB-367 in adult patients with CF. Secondary objectives are to obtain preliminary efficacy data on bacterial density in sputum and pulmonary function following ascending multiple doses of inhaled IB-367 and to monitor for evidence of systemic abortion of IB-367 characterized by vasodilatory response or other toxities. Subjects will be inpatients for 3 days (Day 1-3) for 5 drug doses and safety monitoring. They will return again on Day 6 for a post-study evaluation outpatient visit. We wish to conduct this study at the GCRC to ensure accurate timing of study tests and study drug administration. Conducting this study in the main hospital would be very difficult to do while maintaining strict study schedules.